An elevator installation comprises a plurality of shaft doors and a car door, wherein the shaft doors and the car door each comprise a respective door leaf. A shaft door can be opened or closed by a door drive, which is arranged at the car door, when the car door is coupled with the shaft door. A door closing device is usually arranged at each of the shaft doors so as to be able to close or keep closed this shaft door at all times by means of a closing force.
In the event of failure of the electrical energy supply the door closing device has the effect that the opened shaft door and possibly the car door coupled with the shaft door are closed. Because in that case a holding moment of the door drive is no longer provided, the acceleration forces caused by this door closing device can produce kinetic energy, which lies above legal limits, of the door leaves. That can lead to, inter alia, risk to or annoyance of persons present in the region of the elevator door.
JP-A-2003261281 shows an elevator door with a door leaf and a motor coupled with the door leaf. In the event of failure of the power supply the door leaf is accelerated in closing direction, whereupon the motor generates electrical energy. The electrical energy is converted by means of resistances into heat which leads to braking of the door leaf. However, it is disadvantageous that costly resistances of that kind have to be used. Moreover, it is disadvantageous that regardless of the position of the door leaf there is braking which, in the case of power failure occurring with an at least partly open elevator door, can lead to lengthy closing times.